Failed Fusion Drive.. 2015 5K 27" i7 iMac

[TheRidgeback]

I have a late 2015 5k iMac, 32G 3TB Fusion drive, and until about 8 weeks ago was perfect,
Latest Catalina OS Installed, etc etc.

After the Catalina install I started to notice that it was slowing down a lot, and by a lot I mean 4-5 mins to boot,
4 mins to open email. This was going on for about the last 12 weeks.
After checking my system my Disks were full.... less than 1G spare. (ah ha moment)

So I moved over 2TB of stuff and freed up the disk space.

Didn't make any difference to the speed of the machine, still very very slow.

Now, Sunday I had just finished doing some music editing and left the Mac on as I always do.
Monday afternoon, I was greeted with a black screen. After power cycling it, it went straight to boot camp.

MacOS completely missing, just shows up as unformatted space on first aid.

Now I had no signs of impending HDD Failure, none of the usual clicking or random crashing etc, just a general slow down which I put down to lack of disk space.

So over the last 3 days I've used boot camp to try and access my Disks to see what's happening,
I've even installed Catalina on an external disk, to run loads of diagnostic software.

so using diskutil list
I can still see the following partitions.
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *3.0 TB disk0
1: EFI EFI 209.7 MB disk0s1
2: Apple_APFS 2.8 TB disk0s2
3: Microsoft Basic Data BOOTCAMP 201.4 GB disk0s3
4: Windows Recovery 488.6 MB disk0s4


Neither 1 or 2 will mount using terminal.
could not mount "disk0s2" com.apple.DiskManagement.disenter error -119930868
First aid shows no errors.
recovery works
I can scan on bootcamp the Apple_APFS Partition and see loads of data, which should be recoverable,
So my questions are.

1) Are these disks. 1: & 2: my SSD and HDD and have they failed and defused.
2) If I remove the HDD and replace with a 2TB SSD do I need to be aware of the original SSD and new SSD refusing together?

Im not too bothered by the two weeks data I have lost as I can recover that using windows (hopefully),
I've yet to find any apple software which can even show any data on the drive (any suggestions welcome)

3) should I leave the original SSD in or remove it, being that's its only a small drive and I'm fitting a 2TB one, I don't really want to leave it in as I can't be sure that that's not the one that has failed in the first place.

4) are the SSD that are used in the fusion devices prone to failure?

Its Easy enough as I've got to strip the machine down anyway to replace the HDD so I might as well remove that drive as well.

Cheers

Mac.

 

[JPalomino]

Similar thing happened to me. Same vintage iMac, but running Mojave. Everything was fine, a couple of days ago (July 20-something) booted into Bootcamp, saw there was an Apple upgrade to bootcamp and installed it as usual. Then tried later to reboot into MacOS, and MacOS had disappeared. Booted from external drive, the data seem to be there, but there is no file system accessible on the fusion drive. Must be the SSD because Bootcamp is working well in its partition on the same drive. I'm completely backed up, so no worries, but weird. Did the Catalina-compatible upgrade block or forget about the SSD and the fusion drive? I knew this would happen one day with that drive.

 

[Nguyen Duc Hieu]

As shown in other threads, the 32GB SSD has been used as a cache for the Fusion Drive, and for heavy users, they tend to be overloaded and died without any warning. Replace both drives and re-install OS.
After the machine has been operating well again, you can retrieve your data from SSD/HDD using a USB box.

 

[nambuccaheadsau]

If this is a 3TB platter, the SSD should be 128GB. The 32's only came with the standard 1TB platter.